Showing controls

These bids may only be made from 3 ♠ upwards in the case
of a fit in Hearts, or
correspondingly higher for fits in other suits. For example, after the
sequence 1 ♦,
Pass, 1 ♥, Pass, 3 ♥, Pass, a bid of 3 ♠ shows a
control in Spades. In any other sequence 4 ♣ is the lowest possible
control showing bid